Milling machine for making spiral conical antenna feed



Dec. 2, 1969 A. L. HOLLOWAY MILLING MACHINE FOR MAKING SPIRAL CONTCAL ANTENNA FEED m f w A M y w N mm m N Q Filed Nov. 6, 1967 Dec. 2, 1969 I A. L. HOLLOWAY 3,431,249

MILLING MACHINE FOR MAKING SPIRAL CONICAL ANTENNA FEED Filed Nov. 6, 196'? 5 Sheets-Sheet 2 Dec. 2, 1969 A. L. HOLLOWAY MILLING MACHINE FOR MAKING SPTRAL CONICAL ANTENNA FEED Filed Nov. 64 196'? 5 Sheets-Sheet S Dec. 2, 1969 A. L HOLLOWAY MILLING MACHINE FOR MAKING SPIRAL CONICAL ANTENNA FEED 5 Sheets-Sheet 4:

Filed Nov. 6, 1967 2% /MaA/r Dec. 2. 1969 A. L. HOLLOWAY MILLlNG MACHINE FOR MAKING SPTRAL GONICAL ANTENNA FEED 5 Sheets-Sheet 5- Filed NQv.

US. Cl. 9011.64 2 Claims ABSTRACT on THE DIscLos RE A type of milling machine is shown wherein a horizontal rotating 'barrelcam moves a follower carriage lengthwise of the camby means of an accurately formed non-linear spiral groove in the cam'mating witha cam follower on the carriage. Also carried by the carriage is a cutter which meets tangentially with' the surface of the cone on which the desired spiral paths are formed. 'The cone is rotatably mounted in the machine, about an axis coplanar with the cam axis, and is rotated in desired geared proportion to' the cam, so that thecutter' mills out the desired spiral curve or curves around the cone.

" The present invention relates to precision machinery,

and more particularly, to a means and method of producing non-linear spirals on the surface of a cone, such as electrically conductive spiral paths on conical antenna feeds. Such feeds are especially useful in theUHF range.

In order to provide a wide band antenna for radar or the like, it is common to use one or more conical feed members near. thefocus of a reflector dish, the feed members each having a pair of interwoven logarithmic spiral conductive paths located thereon. The efficiency of the antenna operation is directly dependent upon the accuracy of the spiral conductors, andv presently known meth- Ods;f manufacturing the conical spiral conductors, such as wrapping with wire, result in very low efficiency. It .is an object of the present invention to providea means and-method of producing a very accurate geometry of the spiral conductorson the non-conductive conical surface. It is a further object to provide such a conical spiral in an economical and practical fashion, so that higher efficiency is obtained without increased cost.

Briefly as to method, my inventioncomprises first making a cam-like member or mechanism havinga predetermined exponential curve shape or, output movement which is then used to guide a cutter or'marker over the correct path on the surface of a rotating metal-clad nonconductive cone tocut or trace a desired logarithmic spiral curve. When producing'a final cone having two 180 displaced conductive paths thereon, four identical narrow curved-grooves are formed substantially 90 apart around the circumference of the cone, and then the material-between two opposite pairs of curves is removed to leave the final two correctly shaped spirals.

Briefly as to apparatus, my invention comprises a type of milling machine having asynchronously rotated cone- .holder and cam, a cam follower, and a cutting tool which moves with the cam follower and engages the surface of the cone on which the desired spiral paths are to be provided. From the desired conical spiral curve or curves, and the selected type of cam mechanism and component relations, the required cam curve can be mathematically derived, and such cam is very accurately made by means of an electronic computer-controlled machine, for example. The cutting tool is driven by a high speed motor. Adjustments are provided for accommodating a variety of cone angles. A reversing mechanism is preferably included between the cam drive and the cone drive so that United States Patent 0 ice either right-hand or left-hand spirals may be produced on the cone. Also, an automatically-controlled variable speed drive is preferably provided to obtain essentially constant linear cutting speed at the cone surface.

The present invention will be more fully understood by reference to the detailed description of a specific embodiment to follow, and to the accompanying illustrative drawings thereof.

In the drawings:

FIGURE 1 is a plan view of the complete conical spiral cutting machine.

FIGURE 2 is a sectional elevation view of the machine taken as indicated by broken line 22 in FIGURE 1.

FIGURE 3 is a left end view of the same machine.

FIGURE 4 is a perspective view of the top portion of the machine, showing arrangement of the cam follower carriage and parts thereon relative to the conical workpiece.

FIGURE 5 is a perspective view of a finished cone, showing the spirals produced thereon.

FIGURE 6 is a cross section of the cone taken perpendicular to the cone axis as substantially indicated by broken line 6-6 in FIGURE 5.

Referring first to FIGURES 1 and 2 for a detailed description of one preferred form of apparatus embodying the invention, the machine comprises a structural frame-Work 1, a horizontal bed 2 on which two parallel ways 4 are mounted, a tool carriage 5 slidably mounted on ways 4, an end plate 6 carrying power components, and an angular cone support frame 7.

On the end plate 6 is mounted a drive motor 9 coupled by a variable speed unit 10 to an output unit 11 (FIG- URE 3) having a drive shaft 12 extending horizontally through end plate 6. Under bed 2, shaft 12 carries a first drive gear 14 and also drives a constant-speed universal joint 15 attached in turn to a cone drive assembly 16 which is mounted on the cone support frame 7. The left end of support frame 7 carries two upstanding angle plates 17 which are pivotally hung by bolts 19 from mounting gussets 20 in turn rigidly attached to end plate 6. An important feature is that the pivot axis of the frame 7, as represented by the connecting centerline between bolts 19, passes exactly through the operative center of the universal joint 15, indicated as point P in FIGUREZ. Fore more rigidity, a brace 21 is connected from each gusset 20 to a lower portion of thebed 2. p

At the right-hand (upper) end of cone support frame 7, the tubular sides thereof slant inwardly to'a central position where they are joined and are bolted "to a bracket 22 adjustably' attached to the lower side of'bed 2. I

The bracket 22 contains a short slot 24, and a lock bolt 25 passes through this slot and also through a long vertical slot 26 in a stationary hanger 27.' A handle-operated screw shaft 29 threads througha nutmernber 30 pivotally attached to bracket 22,"the handle end being seated in'a spherical washer 31. It is thus seen that the upper end of Come support frame 7 is vertically adjustable, for the purpose of handling cones of variousapex angles up to a design maximum.

At the lower end of support frame 7, the cone drive assembly 16 comprises an indexing plate 32 and associated members, through which is driven an adapter section 34 having a flange 35 to secure to the base of a cone to be installed, the cone being indicated by phantom lines 36. At the upper end of frame 7, a retainer 37 on an extension 39 of an axial shaft 40 is adapted to threadably clamp against the apex end of cone 36 for support thereof. Extension 39 is mounted in a dead center 41 in a conventional type of clamp post 42.

It will be noted that the upper surface of the cone 36 is horizontal, i.e., parallel to the ways 4. For other cone angles, the length of adapter section 34 can vary, and the height of bracket 22 changed to accommodate.

Continuing with the power train, a second drive gear 44 meshes with first drive gear 14, and this second gear 44 drives a set of further gears on the outside of end plate 6, as shown in FIGURES 2 and 3. The latter gear group contains a reverse idler gear 45 and associated shifting arms 46 and 46a for bringing this gear into play to reverse the driven direction of a cam drive gear 47 with respect to direction of drive motor and cone rotation.

Cam drive gear 47 is attached on the shaft of a barrel cam 50 rotatably mounted in bearing 51 on top of the bed 2 and extending substantially the full length of the machine. Cam 50 is provided with a control groove 52 designed to suit the particular job at hand.

FIGURE 4 shows details of the right-hand side of the carriage and its action relative to cam 50. Here, a sliding plate 54 is mounted directly over cam 50, and is adjustably controlled lengthwise by a manual crank 55 (FIGURE 1). Two knob clamps 56 hold plate 54 in position on carriage 5 after the proper crank adjustment is made.

A follower stem 57 extending from the bottom of plate 54 carries a cam follower 59 which is positioned to fit snugly into cam groove 52 so that when the cam 50 is revolved, the follower 59 pushes the carriage 5 along the ways 4 accordingly. Also depending from carriage 5 is a cutter shaft 60 positioned over the centerline of the cone 36 to be processed. The lower end of cutter shaft 60 carries a vertically oriented high-speed cutter motor 61 in which is mounted a cylindrical shaped cutter 62 arranged to contact the surface of cone 36 and perform the required cutting operation as the cam and cone are revolved. Cutter motor 61 may be operated independently of the cam drive.

A cone 36 made according to this invention as a antenna feed member is shown in FIGURE 5. A typical conical antenna feed may have a cone apex angle of 25 to 30, for example, and the spiral curves make an angle of about 80, for example, with the slant lines drawn on the cone surface from the apex. As inserted into the machine, cone 36 comprises a non-conductive body 64 having a complete covering of a copper foil 65, for example, this foil being bonded to body 64 by a conventional bonding material. Alternatively, a copper or other conductive coating may be provided on the cone body by a deposition process or the like.

Knowing the equation of the log spiral curve(s) required on cone 36, the necessary spiral groove 52 in the cam 50 is determined. Then, cam 50 is preferably manufactured on a precision type of electronic computer-controlled machine. Thus, a master cam is produced, by means of which many conical spirals can be made on the present machine. Of course, the conical feeds could also be produced on the computer-controlled machine, but it would be obviously complex, slow, and very expensive.

In operation, the cone 36 with its electrically conductive surface is installed in the present machine with its upper surface line horizontal and at a convenient height with respect to cutter 62. Cutter shaft 60 can be regulated in height by means of a thumb screw 66 and clamping screws 67 so that the cutter will reach a depth equal to the thickness of the conductive coating or foil 65. The carriage 5 is set at one end of cam groove 52, and the machine is then operated to make one complete narrow spiral cut around the cone 36. As shown in FIGURE 2, a rotating follow-up cable within a flexible shaft 69 is connected between the cam 50 and the variable speed unit 10. As the cam rotates, the speed of drive motor 9 is thus automatically varied in the proper sense to maintain linear cutting speed at the cone surface substantially constant. This is advisable due to the changing diameter of the cone as the operation proceeds. The variable speed unit is a standard unit available for speed control. As

a control element (not shown) of the unit 10 is rotated, the output r.p.m. of the unit 10 is varied relative to the input r.p.m. (as driven by motor 9). Since the shaft of cam 50 is being continuously rotated during operation, the follow-up cable in flexible shaft 69 is continuously turning the control element of the variable speed unit 10. As the carriage 5 is moved to the left (viewed in FIGURE 2) toward the large diameter of the cone 36, the cable in shaft 69 will rotate in the proper direction to reduce the output speed of variable speed unit 10. When carriage 5 is moving to the right, the cable rotation in shaft 69 is reversed to increase the output speed. Variable speed unit 10 by itself is not a part of the present invention.

After one spiral cut is completed, the cone 36 is disconnected at the indexing plate 32 and rotated in preparation for a second cut. At the same time, due to the finite width of the cuts, the sliding plate 54 is adjusted to retard the cutter 62 an amount equal to the cutter diameter. This will be further understood by reference to FIGURE 5, where the small circles 70 and 70a represent the relative positions of the cutter during two adjacent successive cuts to mill out both sides of one space 71. This is necessary since the opposite edges of each conductive path 72 and 72a in FIGURE 5 are to be equally angularly displaced. If different respective widths of the final paths are required, the adjustment of sliding plate 54 can be made accordingly.

Proceeding in this manner, the third and fourth cuts are made, indexing the cone 90 each time between cuts. Then the cone 36 is removed, and the conductive material remaining in the space between the proper adjacent pairs of cuts is stripped out, to leave the finished product as appears in FIGURE 5. FIGURE 6 shows a right sectional view of cone 36, illustrating the two conductive paths 72 and 72a which comprise the two spiral curves spaced apart.

From the preceding description, it is thus seen that a superior conical spiral is obtained by the use of the present invention. The electrical properties are improved over other methods of preparing a conical winding, particularly the anntenna efiiciency, primarily due to the exact relative width and spacing of the conductive paths. Of course, the same principle and basic machinery can be used to produce any desired type of spiral curve on a cone.

Those skilled in the art will realize from the present example that other means may be employed to provide the controlled movement of the cutter 62 in place of the barrel cam 50. For instance, a circular disc cam may be provided with a spiral planar groove therein; or an eccentric type cam with a spiral edge against which a follower travels. Each design can be provided with the necessary mechanical linkages.

Another variation is to mount the cone axis and barrel cam axis parallel, and move the cutter at an angle to the barrel cam using a type of taper attachment. This arrangement would eliminate the need for the universal joint 15.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed cornprise the preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

1. A device for making exponential conical spiral curves, comprising:

(a) a rotatable cam having an exponential spiral control groove therein;

(b) means for mounting a cone for rotation about its axis;

(c) driving means connected to said cam and to said cone for simultaneous rotation thereof;

(d) a linearly movable carriage;

(e) a cam follower mounted on said carriage adapted to move said carriage in accordance with said groove; and

(f) a cutting tool traveling with said carriage and positioned to traverse the surface of said cone during operation of said device;

(g) said cone mounting means including a frame ad- (e) a cam follower mounted on said carriage adapted to move said carriage in accordance with said groove;

(f) a cutting tool traveling with said carriage and positioned to traverse the surface of said cone during operation of said device;

(g) a variable speed drive unit in said driving means, and rotating feedback means connected from said cam to said varriable speed drive unit arranged to reduce the rotary speed of said cam and cone as said justable about a pivot line for varying the angle of 10 cutting tool moves from the apex toward the base inclination of said cone with respect to the direcof id one tion of movement of said carriage; (h) said driving means to said cone having included Refer Ci d there a constant-speed universal joint, the pivot point of said universal joint being on the pivot line of said UNITED STATES PATENTS frame- 2,197,825 4/1940 Nelson 90-11.64 2. A device for maklng exponentlal conical spiral 2593 310 4/1952 Johnson curves, comprising: u

(a) a rotatable cam having an exponential spiral con- DONALD R. SCHRAN, Primary Examiner trol groove therein;

(b) means for mounting a cone for rotation about its axis;

(c) driving means connected to said earn and to said cone for simultaneous rotation thereof;

(d) a linearly movable carriage;

G. WEIDENFELD, Assistant Examiner US. Cl. X.R, 

